The present invention relates to a carbonaceous binder system. More particularly, the present invention relates to a binder useful in carbon containing refractories, and to refractory compositions useful in the formation of shaped or unshaped carbon-containing refractory articles. The present invention also relates to a process for preparing such a carbonaceous binder useful in carbon containing refractories.
Refractory products can be produced as unformed compositions, such as ramming, casting, or gunning mixes, or as preshaped objects, such as bricks. The standard rectangular brick, measuring 9 inches long, 41/2 inches wide, and 21/2 inches thick, is most often used to build straight walls. Tapered bricks which form self supporting arches, and tapered bricks with undercut slots on the exterior side from which the brick may be hung, may be used to form curved walls and roofs of a furnace. In addition to such bricks, special shaped articles have been designed such as corner blocks or edge blocks with curved interior faces, skew block, floor tile, muffle wall tile, and grid sections tile. Moreover, blocks of special shapes may be formed with various shapes and sizes of openings in the block for the insertion of burners and the like. Refractory shaped articles also include runners, gates, sleeves, nozzles, and troughs used to control the flow of molten material.
Bricks and other shaped refractory articles can be formed by hand molding, mechanical pressing, or casting in pre-shaped molds, either as water-based slurries or in molten form. Refractory bricks and other shaped articles have generally been formed from compositions containing refractory components and inorganic binders with or without a carbonizable binding material. The carbonaceous binder serves not only to bond the aggregates together during the manufacturing process, but when the articles (e.g., bricks, ladles, runners or patches) are heated in a steelmaking furnace, the binder decomposes and carbon is deposited within the pore structure of the article and around the refractory aggregate. This carbon residue, resulting from pyrolysis of the carbonizable binder at high temperature, forms a carbon bond between the refractory aggregates. The binder thus provides strength during manufacture and also resistance to slag and metal penetration and wear during use.
Coal tar pitch has previously been employed as such a binding material and continues to represent one of the most economical binding agents. Tars and pitches in general have found particular wide usage as binders for refractory aggregates in basic oxygen steelmaking furnaces, electric arc steelmaking furnaces, and iron and steel ladles. In U.S. Pat. No. 4,521,357 issued to Kernion et al, a combination of a thermosetting resin and pitch is used to even further improve the bond. However, in both bricks and shaped article applications, tar and pitch bonded refractory compositions have been recognized as generating substantial quantities of noxious fumes, including particulate matter and polynuclear aromatic hydrocarbons, during firing. These fumes pose air contamination and occupational health hazards and have been recognized as carcinogenic. Coal tar pitch also presents a hazard during installation resulting from skin contact, inhalation or ingestion.
Efforts have been made, and are continuing to be made, to replace the coal tar pitch binding materials in refractory compositions. For example, U.S. Pat. No. 4,072,531 issued to Funabiki et al. discloses a blast furnace taphole plugging composition including, inter alia, a lignin-modified phenolformaldehyde condensation product as a replacement for some or all of the tar binding material. In reference to prior art efforts to substitute conventional phenolic resins for the coal tar binder in similar compositions, Funabiki et al. note that conventional phenolic resins are disadvantageously expensive.
U.S. Pat. No. 4,022,739, issued to Bove discloses a binder for taphole plugging compositions which does not generate noxious fumes to the degree experienced with coal tar. The binder of Bove comprises a mixture of a high boiling hydrocarbon derivative and a synthetic resin, which may be a phenol-formaldehyde resin having resorcinol molecules in the polymer chain. In this regard, the use of resorcinol-formaldehyde and phenol-formaldehyde polymers as temporary binders for refractory materials including brick is well known. U.S. Pat. No. 3,007,805, issued to Cline and U.S. Pat. No. 2,938,807, issued to Andersen both disclose the use of phenol-formaldehyde and resorcinol-formaldehyde resins as carbonizable binders for refractory bodies.
Use of phenol-formaldehyde and resorcinolformaldehyde polymers as the binding material for refractory compositions, however, does not entirely solve the noxious fume problem. More specifically, these polymers commonly contain free formaldehyde. As noted in U.S. Pat. No. 3,917,558 issued to Gardikes et al., the formaldehyde vapors generated during curing are unpleasant, irritating, and pose a health hazard to persons continually exposed to such vapors. Moreover, these polymers may contain 5-10% free phenol, which may also vaporize during curing and thus generate toxic fumes. In addition, fumes from organic solvents employed with prior art synthetic resin binders are hazardous to manufacturing employees.
U.S. Pat. No. 4,387,173 issued to Henry, Jr. et al discloses compositions for forming carbon-containing refractories which overcome many of the noxious fume problems encountered with the use of coal tar binders and conventional phenol-formaldehyde resins as binders. The composition comprises a refractory filler, a binder for said filler and a hardening agent for said binder, with the binder comprising a mixture of polymers formed by the homopolymerization of resorcinol.
The use of sugars has also been suggested for use in refractories. For example, the use of a composite cross-linking agent/resin former composition as a resinous binder for foundry sands is disclosed in U.S. Pat. No. 3,551,365 issued to Matalon. The resinous binder composition comprises a reducing sugar, as well as water, a polyhydric phenol (e.g. resorcinol) and phosphoric acid. The composition can be generally prepared by dissolving the reducing sugar in water, then adding the polyhydric phenol and phosphoric acid. The system is then brought to a boil and maintained at about 115.degree.-116.degree. C. for a period of five to ten minutes. The resulting mixture can then be reacted with furfuryl alcohol or a furfuryl alcohol-formaldehyde resin to form the resinous binder. The high acidity of the binder, however, has been found to cause some problems For example, the shelf-life of the binder or binder/aggregate is found to be unacceptably short, only about 2 weeks. Whereas a shelf-life of at least 1 month, and preferably 3-6 months is desirable. Moreover, troublesome reactions can occur between the binder and the impurities found in SiC (silicon carbide) and/or fused bauxite found in many refractory aggregates. The odor of furfuryl alcohol also makes this binder undesirable for use in the steelmaking environment. Such difficulties can limit the effective range of use of such binders.
See also U.S. Pat. No. 4,396,430 issued to Matalon which discloses a composition useful as an adjuvant for silicate bonded sands. The adjuvant is obtained by reacting a reducing sugar, an optional dicarboxylic acid or acid anhydride and boric acid.
The use of a reducing sugar and phosphoric acid reaction product with a hardener is disclosed in U.S. Pat. No. 4,265,963 issued to Matalon. Therein, the resulting polymeric material is used as a coating for flameproof and fireproof products. This binder also has limited ability because of its high acidity.
Therefore, while the art of carbonaceous binder systems has proposed to overcome many of the problems inherent in working with the early toxic-and noxious binder systems for refractories, the replacement systems which are non-toxic and non-irritating have been found to typically yield lower carbon residues and have inferior properties after coking, among other problems. Improvements in these functional areas are needed to enhance the commercial validity of a non-irritating binder system.
Accordingly, it is an object of the present invention to provide a novel, improved carbonaceous binder having a wide range of effective refractory applications.
It is still another object of the present invention to provide such a carbonaceous binder which has a comparatively high carbon yield upon pyrolysis.
Yet another object of the present invention is to provide such a novel carbonaceous binder which exhibits excellent shelf-life.
Another object of the present invention is to provide a novel refractory composition comprised of a carbonaceous binder which is non-irritating, exhibits good shelf life, and provides a high carbon yield upon pyrolysis of the binder solids.
Still another object of the present invention is to provide a novel process for preparing such an improved non-irritating carbonaceous binder.
These and other objects of the present invention will become apparent upon a review of the following specification and the claims appended thereto.